When a user takes a picture by a still camera, for example, in the dark because it is difficult for a user to visually confirm an object, the object cannot be brought into focus by an auto focus camera, for example, of a contrast detection type. It is also difficult to bring the object into focus in a manual focus mode. To solve this problem, there has been employed so far a method which enables an auto focusing operation by irradiating the object with an auxiliary floodlight such as an LED. According to this method, however, when an object has low contrast, it used to be difficult to bring the object into focus.
On the other hand, for example, a floodlight for producing a large output required for obtaining the brightness enough to focus on the object consumes large electric power and thus produces such a great deal of heat that the floodlight cannot be used near the object. Alternatively, there is known, for example, a method in which light is condensed by a lens to floodlight an object. However, when light is condensed into a narrow area in order to increase the brightness of an object, if a user takes a picture using a wide-angle lens, then a floodlighted area will be too narrow to make focusing easily. Conversely, if the floodlighted area is made so wide as corresponds to that in the wide-angle photographing, a sufficient brightness of the object cannot be obtained disadvantageously.
Further, while there is employed an auxiliary floodlight in which a lens and a slit are placed in front of an LED or an electric bulb, etc. to project an image of the slit onto the object, a projected image has low contrast, so that satisfactory focusing is made difficult. Moreover, according to this method, light loss is unavoidably produced in the floodlight due to the slit, and hence electric power consumption for obtaining a necessary quantity of light is extremely large. As a result, it is difficult for the above-mentioned auxiliary floodlight to be incorporated into, for example, a small electronic still camera and driven by a power supply such as a built-in battery.
Aside from these prior arts, there has been proposed an image projection apparatus in which an arbitrary hologram reproduced image is projected by using, for example, a laser light source and a hologram plate. Such hologram reproduced image can enhance contrast of a projected image. Accordingly, it is conceived that this hologram reproduced image is projected onto an object to be made use of focusing. That is to say, the detection in the manual focus mode or in the auto focus mode is performed using the hologram reproduced image that is projected onto the object.
However, the image projection apparatus is such that a hologram plate is added to the existing so-called “laser pointer”, the structure of which is shown in FIGS. 14A and 14B, for example. Specifically, as shown in FIG. 14A, a laser light source 71 for generating light of diffused laser beams and a condenser 72 for converting the light of diffused laser beams to light of parallel laser beams are provided within a lens barrel 70. The light of parallel laser beams converted by this condenser 72 is used as a laser pointer for indicating an arbitrary point and so on.
A hologram plate 73 is provided within a lens barrel 74 which is fitted onto the lens barrel 70. Then, when the light of parallel laser beams is applied to this hologram plate 73, a hologram reproduced image is formed and projected onto the object. However, in this image projection apparatus, the laser light source 71 and the condenser 72 are integrated with each other as a single unit by the lens barrel 70, and the hologram plate 73 of the lens barrel 74 is added to this unit thus formed. When the lens barrel 74, for example, is broken, there is a risk that only the hologram plate 73 may be detached from the unit.
Accordingly, when the hologram reproduced image is projected onto the object to be used for focusing as described above, if only the hologram plate 73 is detached from the unit and the light of parallel laser beams from the condenser 72 is directly applied to the object as shown in FIG. 14B, then the object, for example, a man will feel discomfort due to a dazzling light of parallel laser beams if he sees it. When the hologram plate 73 is present, the hologram reproduced image is formed and hence light of laser beams is diffused, so that the discomfort given to a man will be alleviated.
The present invention is made in view of the aforesaid points and the problems to be solved is as follows: When a user takes a picture by a still camera in the dark, for example, it is difficult for the user to focus in the auto focus mode of the contrast detection system or in the manual focus mode. On the other hand, the camera apparatus using the conventional auxiliary floodlight does not allow a satisfactory focusing to be performed. Moreover, because the conventional auxiliary floodlight consumes large power, it cannot be incorporated into a small electronic still camera for use.
Furthermore, the image projection apparatus using, for example, the laser light source and the hologram plate has a risk that, when the hologram plate is detached and so forth, a man as an object will feel uncomfortable very much due to a dazzling light of parallel laser beams if he sees it.